text: Studies of other herbivore midden remains have been very effective in palaeoenvironmental studies in dryland regions on several continents. In the southwestern United States pack rat middens have provided an unprecedented record of environmental changes over the last 40,000 years. As a result of this work, the vegetation dynamics of this area are some of the best understood for any of the world’s drylands at this timescale, and the critical data provided have dramatically helped define the range of regional climate variability. This work has also led to important perspectives on ecological theory, which have impacted on management strategies by allowing a distinction to be made between anthropogenic environmental impacts and natural processes.
  Midden studies have also been undertaken in Australia  and South America. This work has highlighted a fundamental difference between middens from these regions and hyrax middens. American and Australian middens are essentially nests composed of sticks and other macrobotanical remains. These middens are generally reported have no clear stratigraphy, and researchers have thus adopted the methodology of processing them as single samples that provide a palaeoenvironmental snapshot. Hyrax middens, on the other hand, are primarily urino-fecal deposits, and are deposited progressively as a series of layers. This diachroneity is one of the fundamental advantages of hyrax middens over nest middens, which are only secondarily preserved as the animals urinate in their shelters.
  Examinations of the internal and external structure of hyrax middens suggest flow/deposition dynamics similar to speleothems (cave deposits, e.g. stalactites), with the fresh urine flowing across the surface of the midden, then drying and crystallising, preserving the stratigraphic integrity of the midden. The general morphology of middens is often characterised by (1) lobate forms, (2) undulating weathering features on exposed midden faces, and (3) in some cases the formation of thin (1-3 mm in diameter) stalactites on the underside of some middens. As a result, questions over the potential for post-depositional remobilisation of hyraceum may be raised. The examination of over 150 middens, however, has confirmed the visible stratigraphic integrity of the middens, and while some surficial alteration of exposed surfaces can occur, consistently coherent age-depth models, and the nearly vertical exposed external faces of the middens indicate that, once dry, hyraceum is not prone to significant remobilization.